In each case according to the structural configuration of the pumping heads conventionally used for exhausting compact fluorescent lamps, the pumping process is matched to the lamps having one exhaust tube or two exhaust tubes. (Exhaust tubes are also known as `tubulation` but the former term is preferred herein.) In a known type of fluorescent lamp there is a single exhaust tube at one end of the light tube, while the current conductors (lead-in wires) and electrodes (cathodes) are built into both ends of the light tube. During the pumping process the light tube is exhausted via this single exhaust tube and filled with gas and mercury is dosed in. The pumping head used here is suitable for realizing a cyclical exhausting and flushing process, which means that in several alternating steps exhausting (or pumping; these terms being synonymous and used interchangeably herein) and flushing follow each other in a sequence of operating stages until the interior of the discharge vessel attains the desired gas purity.
Japanese Patent Specification No. 55-157918 describes, for example, a pump head construction which is suitable for the automatic realization of such a cyclical pumping process.
However, this process requires a significant expenditure of time and unnecessarily prolongs the duration of the operation of the pumping process (exhaustion and cathode activation); moreover, it cannot assure the required vacuum purity at the exhaust tube ends during cathode activation. From the nature of this method a further disadvantage follows, namely that the gases resulting from the cathode activation from the end without exhaust tube must be exhausted through the other end which does have an exhaust tube. The cathode at the end with the exhaust tube becomes thereby exposed to the dissociation gases, which not only make it difficult to activate the cathode but may also cause it to be poisoned.
According to another known solution the compact fluorescent lamp is equipped with two exhaust tubes with one respective tube at each end, whereby the two exhaust tubes in the suction head are alternatingly and simultaneously exhausted, as is the case in the solution with one exhaust tube. In comparison with the solution with a single exhaust tube, the solution with two exhaust tubes has the advantage that both cathodes have the same position relative to the gas flows. Apart from that, however, here also the cycle of exhausting and filling must be performed repeatedly, which is time-consuming. In the case of long and straight light sources a rapid pumping process is used which is based on continuous gas flushing. Through one exhaust tube at one end of the fluorescent lamp pure flushing gas is introduced into the discharge vessel of the lamp, while at the other end it is exhausted. This method, which is described in detail in Hungarian Patent Application No. 204/87, allows the duration of the operation of exhausting and cathode activation to be reduced to a minimum.
This exhausting process could also advantageously be used for compact fluorescent lamps. The currently existing pumps do not, however, afford this possibility because the two tightly adjacently arranged limbs of the discharge vessel of the compact fluorescent lamp, with the exhaust tubes at the ends of the limbs, fully exclude the possibility of connection to the pumps, as is conventional with straight fluorescent lamps.